A case-control study of female breast cancer will be undertaken in the two largest hospitals serving residents of Long Island, a high-risk geographical area in New York State, in order to investigate new leads in breast cancer etiology. The primary aim is to study breast cancer risk in relation to levels of organochlorine compounds such as polychlorinated biphenyl (PCBs) and several once-common pesticides. Levels of these compounds will be measured in adipose tissue of breast cancer cases and two sets of matched controls, one consisting of women with benign breast disease and the other of women undergoing a variety of surgical procedures. A secondary aim is to study possible associations of breast cancer with (a) consumption of foods whose of preparation endows them with high levels of polycyclic aromatic hydrocarbons (PAH) and heterocyclic aromatic amines (HAA); (b) estrogen replacement therapy, especially in lean women; (c) occupational and other exposure to radiofrequency electromagnetic radiation; (d) other possible risk factors, such as heavy alcohol consumption.